DHPG or B759U are identical acyclovir congeners which have excellent in vitro activity against cytomegalovirus, a frequent cause of disease in immunosuppressed patients. Studies have been carried out to assess its efficacy in patients and its toxicity. These stuides appear to be one of the few organized trials assessing this promising compound. AIDS patients with CMV retinitis, colitis, or pneumonities have been treated. Retinitis responded dramatically in 9/10 patients, as did colitis in 2/3 patients and pneumonitis in 1 patient. 10/11 patients converted blood cultures from positive to negative. Bone marrow toxicity was noted to be severe in three patients. Clinical and virologic relapses occurred within several weeks of stopping therapy. One non-AIDS patient with CMV retinitis has been successfully treated and has not relapsed during 5 months of followup. The significance of this study is that it is the first evidence of effective therapy for CMV disease. A randomized cross over study to confirm these is scheduled to begin.